The invention relates to a temperature measuring device for the furnace of a metal caster, the device including a crucible holding the metal melt to be measured and covered by a controlled atmosphere bell, with the temperature measuring device being an electro-optical radiation pyrometer including an infra-red (IR) diode for detecting the thermal radiation of the metal melt.
When metals are melted for casting, it is very important to prevent the access of air to the metal melt, particularly because of the differences in moisture content. Known metal casting devices are therefore provided with a controlled atmosphere bell above the crucible holding the metal melt so as to assure a closed controlled atmosphere above the metal melt.
On the other hand, for the production of perfect casting results, it is very important to always know the precise temperature of the metal melt in the crucible. However, the production of the above-mentioned controlled atmosphere by means of the controlled atmosphere bell brings with it the difficulty of measuring the liquid metals disposed in the metal melt in the controlled atmosphere bell with respect to their temperature.
Thermocouples are known for this purpose which are guided into the metal melt from the top through the controlled atmosphere bell. However, this solution has the drawback that if such a temperature measuring device breaks, the contents of the crucible, for example a gold alloy, are soiled and can no longer be used without resorting to a refining plant.
Another known solution therefore provides the use of a radiation pyrometer for temperature measurements. Such a pyrometer is known to be suitable and also adapted for measuring the radiation of a "blackbody". In practice, however, the object to be measured is not an ideal blackbody but a metal surface in solid or liquid state, with or without an oxide layer and additional surface movement in inductive melting processes.
Although the temperature measuring devices employing radiation pyrometers operate relatively without inertia, due to the stated deviations from the ideal state of the blackbody, they operate somewhat imprecisely. This has brought about difficulties again and again in the realization of reproducible smelting processes and casting temperatures.